Due to the world's depleting reserves of fossil fuels such as oil, there exists a need for alternative fuel vehicles(AFV's). The Energy Policy Act (EPACT) signed by President Bush in 1992 requires that states and the federal government take steps to reduce energy use and to shift to other sources of energy, including the addition of alternative fuel vehicles(AFV's) to federal and state fleets. Individual states such as California and New York have instituted goals of near-zero emission standards for percentages of new vehicles sold within those states in the near future. Thus, the need exists for alternative fuels.
Natural gas has long been considered an excellent alternative fuel since it is considered much cleaner than other fossil fuels such as oil, and its reserves are much larger than crude oil. Natural gas is primarily composed of methane and combinations of Carbon Dioxide, Nitrogen, Ethane, Propane, Iso-Butane, N-Butane, Iso Pentane, N-Pentane, and Hexanes Plus. Natural gas is a renewable energy source since anaerobic bacterial eventually will convert all plants into methane type gas. Natural gas has an extremely high octane number, approximately 130, thus allowing higher compression ratios and broad flammability limits.
A problem with using natural gas is reduced power output when compared to gasoline, due mostly to the loss in volumetric efficiency with gaseous fuels, as well as the lack of the infrastructure for fueling natural gas vehicles. Another problem area is the emissions produced by these natural gas vehicles. Although, the emissions are potentially less than that of gasoline vehicles, these vehicles generally require some types of emissions controls such as exhaust gas recirculation(EGR), positive crankcase ventilation(PCV), and/or unique three-way catalyst. A still another problem with using natural gas vehicles is the slow flame speed which requires that the fuel be ignited substantially before top dead center (BTDC). In general, most internal combustion engines running on gasoline operate with a spark advance of approximately 35 degrees BTDC where as the same engine operating on natural gas will require an approximate advance of 50 degrees BTDC. The slower burn rate of the fuel results in reduced thermal efficiency and poor burn characteristics.
Proposed alternative fuels utilizing hydrogen and fossil fuels have also been used with resulting problems. In an article entitled Houseman et at., "A Two-Charge Engine Concept: Hydrogen Enrichment" SAE Paper #741169 (1974), research was conducted at the Jet Propulsion Laboratory. The researchers ran a V-8 internal combustion engine on a mixture of gasoline and hydrogen. The addition of hydrogen allowed the engine to be operated much leaner than was possible on gasoline alone. The result of this research was that NO.sub.x emissions were reduced below the 1977 EPA standard of 0.4 gm per mile. The article states that "At an equivalence ratio of 0.53, very low NO.sub.x and CO were produced and engine thermal efficiency was substantially increased over stock gasoline configurations. The article mentions that in order to "operate a vehicle on fuel mixtures of gasoline and hydrogen, an onboard source of hydrogen is required. Onboard storage of hydrogen, either as a compressed gas, as a liquid at cryogenic temperature, or as a hydrode is not a practical solution today. Direct generation of hydrogen from gasoline in an onboard reactor was selected as the best solution to the problem." The main problem with this device was that the reactor described has not been adopted due to the complexity of the device.
The articles by MacDonald, J. S., entitled "Evaluation of the Hydrogen Supplemented Fuel Concept with an Experimental Multicylinder Engine" Automotive Engineering Congress and Exposition, SAE Paper #760101 (1976), and by Parks, F. B., entitled "A Single-Cylinder Engine Study of Hydrogen-Rich Fuels" Automotive Engineering Congress and Exposition, SAE Paper #760099 (1976) were by authors from General Motors that also investigated the use of hydrogen-enriched gasoline. Reflecting on Houseman et al.'s work, MacDonald states that, "while this approach (hydrogen reactor) as been shown to be feasible, it does have its limitations. A problem is the maximum theoretical yield of hydrogen per pound of fuel is about 14% by weight. Another problem is the hydrogen generator is at best only 80% efficient, so that any gasoline going to the generator represents an efficiency loss, which is a loss in fuel economy. For these reasons it is desirable to keep the quantity of hydrogen required for acceptable engine operation to a minimum. This article goes on to report that when 14.4% of the fuel mass was hydrogen the engine operated satisfactorily with an equivalence ratio of 0.52 and the NO.sub.x levels had dropped below the EPA mandated level of 0.4 gm per mile.
Several U.S. patents have incorporated similar concepts. For example, U.S. Pat. No. 4,376,097 to Emelock describes a hydrogen generator for motor vehicles. U.S. Pat. No. 4,508,064 to Watanabe describes a customized engine for burning hydrogen gas. U.S. Pat. No. 5,176,809 to Simuni describes a technique of producing and recycling hydrogen from exhaust gases.
Some research has been conducted for combining hydrogen and natural gas as a fuel mixture. Articles by Nagalingam et al. entitled: "Performance Study Using Natural Gas, Hydrogen-Supplemented Natural Gas and Hydrogen in AVL Research Engine", International Journal of Hydrogen Energy, Vol 8, No. 9, pp. 715-720, 1983; Fulton et al. entitled: "Hydrogen for Reducing Emissions from Alternative Fuel Vehicles" 1993 SAE Future Transportation Conference, SAE Paper from Alternative Fuel Vehicles" 1993 SAE Future Transportation Conference, SAE Paper #931813, (1993) and an article by Yusuf entitled: "In Cylinder Flame Front Growth Rate Measurement of Methane and Hydrogen Enriched Methane Fuel in a Spark Ignited Internal Combustion Engine, Unpublished Masters Thesis, University of Miami (1990) each disclosed such combinations of a fuel mixture. However, the mixtures were generally limited to 20% hydrogen and the rest generally methane.
U.S. Pat. No. 5,139,002 to Lynch et al., states that hydrogen enriched mixtures should only contain mixtures of up to levels of between "10 and 20%" hydrogen. See column 9, lines 49-60, and column 16, lines 14-21. At column 9, lines 37-60, Lynch et al. states that "Relatively few tests were necessary to rule out the 25% and 30% mixtures (of hydrogen) . . . ."
Despite its clean burning characteristics, the utilization of hydrogen has had many problems as an alternative fuel. Primarily, the use of hydrogen in vehicles has been limited by the size, weight, complexity and cost of hydrogen storage options as well as the cost of hydrogen.